In general, continuous ink jet printing apparatus have a printhead manifold to which ink is supplied under pressure so as to issue in streams from a printhead orifice plate that is in liquid communication with the cavity. Periodic perturbations are imposed on the liquid streams, such as vibrations by an electromechanical transducer, to cause the streams to break-up into uniformly sized and shaped droplets.
A charge plate, comprising an array of addressable electrodes, is located proximate the streams break-off points to induce an electrical charge, selectively, on adjacent droplets, in accord with print information signals. Charged droplets are deflected from their nominal trajectory. For example, in a common, binary, printing mode, charged or non-print droplets are deflected into a catcher device and non-charged droplets proceed to the print medium.
A variety of catcher devices have been developed as constructions to intercept and recirculate the non-print droplets from such printheads. The catcher devices must take several potential problems into account. First, the catcher device must intercept the non-print ink droplets in a way that avoids splattering them onto the print medium, or scattering into an ink mist, which can also cause defects on the print media. Second, the catcher devices must effectively remove the caught ink away from the droplet interception zone so that a build-up of ink on the catching surface does not block the flight path of printing drops.
Planar charging continuous ink jet printers require a catcher to gather deflected drops of ink and assist their return back into the system. Drops that are not caught form printed images. Current art requires a precision metal catcher to achieve the functional specifications for continuous ink jet printing.
However, use of precision machined metal has several adverse attributes. For example, only inert, low coefficient of thermal expansion (CTE), and structurally stiff metals machined to precise tolerances prove effective in meeting functional requirements for continuous ink-jet drop catchers. These requirements render high volume processes and inherently weak polymers useless for catchers. Secondly, conventional machining used to produce metal catcher geometry is constrained by tooling. This constraint means that the diameter of a cutter and/or its run-out that produces a part must be incorporated into the design. More times than not, this compromises basic ink-jet performance of a catcher. Prior art catcher face geometry molding has been limited to rigid thermo-set epoxies. These epoxies cannot be molded more than 1.5 inches in length without face flatness tolerance degradation that is at least twice the acceptable limit for new, higher speed and higher resolution inkjet printers. These epoxy parts are also not suitable structurally or thermally for printing array lengths greater than two inches.
Also, costs associated with conventional machining to obtain prior art are tremendous. The catcher component alone is as much as 17% of the cost of an entire continuous ink-jet print head. Finally, any damage or wear on a catcher face renders the part useless because of the difficulty associated with resurfacing compromised areas.
It is seen then that there is a need for a cost reduced catcher suitable for use with a continuous ink jet printer, that overcomes the adverse attributes associated with prior art catcher designs.